1. Field of the Invention
The present invention relates to the art of axle/suspension systems for vehicles. More particularly, the invention relates to the art of trailing or leading arm air-ride axle/suspension systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers, which cushion the ride and stabilize the vehicle during operation. Still more particularly, the invention relates to an axle/suspension system that includes a composite beam and a pair of separately pultruded brackets. The composite beam has an internal support with vertical stitching to minimize delamination, which is lightweight and maintains rigidity of the beam while still maintaining flexibility.
2. Background Art
Heavy-duty vehicles that transport freight, such as tractor-trailers or semi-trailers and straight trucks, typically include leading or trailing arm air-ride suspension assemblies that connect the axles of the vehicle to the frame of the vehicle. These air-ride suspension assemblies use air springs to cushion the ride of the vehicle. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to a slider box, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle primary frames, movable subframes and non-movable subframes.
In the heavy-duty vehicle art, one or more axle/suspension systems usually are suspended from a single slider box. It is understood that a slider box outfitted with usually two axle/suspension systems typically is referred to as a slider tandem, and for purposes of convenience and clarity, will hereinafter be referred to as a slider tandem. Of course, a slider box may also be outfitted with a single axle/suspension system, or three or more axle/suspension systems. By way of example, reference herein shall be made to a slider tandem having a pair of axle/suspension systems mounted thereon, with the understanding that such reference also applies to a slider outfitted with one, three or more axle/suspension systems. The slider tandem in turn is mounted on the underside of the trailer primary frame, and is movable longitudinally therealong to provide a means for variable load distribution and vehicular maneuverability.
More specifically, the amount of cargo that a trailer may carry is governed by local, state and/or national road and bridge laws, and is dependent on proper load distribution. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry as well as limit the maximum load that can be supported by individual axles. A trailer having a slider tandem gains an advantage with respect to laws governing maximum axle loads. More particularly, proper placement of the slider tandem varies individual axle loads or redistributes the trailer load so that it is within legal limits.
A slider box or other subframe typically includes a pair of longitudinally-extending, parallel, transversely-spaced elongated main members. A plurality of longitudinally-spaced parallel cross members extend transversely between and are attached to the main members. Pairs of transversely-spaced hangers are mounted on and depend from the main members and selected ones of the cross members. An axle/suspension system typically includes a pair of transversely-spaced trailing arm beams, each of which is pivotally connected at its front end to a respective one of the hangers. Each trailing arm beam also is welded or otherwise rigidly attached at its rear end to a transversely-extending axle of the axle/suspension system. The wheels of the vehicle are rotatably mounted, as known in the art, to opposing ends of the axle. The axle/suspension system further conventionally includes a pair of air springs, which each extend between and are mounted on the rear end of a respective one of the beams and a respective one of the main members, and a pair of shock absorbers, which each extend between and are mounted on a respective one of the beams and a respective one of the main members. It should be noted that, while the hangers are sometimes considered to be part of the vehicle frame once they are connected to the frame members, they are typically engineered as part of the axle/suspension system.
The axle/suspension system of the heavy-duty vehicle also acts to cushion the ride and stabilize the vehicle. More particularly, as the vehicle is traveling over-the-road, its wheels encounter road conditions that impart various forces, loads and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental effect of these forces on the vehicle as it is operating, the axle/suspension system is designed to absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle, and side-load and roll forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts and to provide compliance so that the components of the axle/suspension system resist failure.
In the past, prior art beams were formed of a rigid, heavy material such as steel and was connected to a hanger with a compliant bushing. The rigid, heavy material undesirably led to increased weight to an axle/suspension system that undesirably increased operating costs.
In order to decrease weight, prior art composite beams were developed for axle/suspension systems. Prior art composite beams desirably reduced weight to the axle/suspension system but included some other disadvantages. First, some prior art composite beams can delaminate over time, which is the separation of the composite layers. Delamination is undesirable because it compromises the structural integrity of the beam. As a result, it is desirable for a suspension assembly for an axle/suspension system having composite beams to minimize possible delamination of the beam.
In addition, prior art composite beams often employ expensive manufacturing processes, such as vacuum injection molding and reaction injection molding, and other techniques known in the art. Such prior art processes make composite beams undesirably expensive to employ. As a result, it is desirable for each composite beam of an axle/suspension system, including a bushing end housing and axle connection housing, to be manufactured through a cost-effective process.
Therefore, a need exists in the art for an improved axle/suspension system which balances the rigidity of the composite beam to minimize the sway experienced by the vehicle, with flexibility to assist in cushioning the vehicle from vertical forces. Further, it is desirable to minimize the potential likelihood of delamination of the composite beam which can possibly occur over time in composites. In addition, it is desirable to manufacture a composite beam, including a bushing end housing and an axle connection housing, via a cost-effective process. The heavy-duty vehicle axle/suspension system with composite beam of the present invention satisfies these needs, as will be described in detail below.